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How is Work and Power Related? Chapter 5 Work and Power

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How is Work and Power Related? Chapter 5 Work and Power Goals: define and calculate work, energy, kinetic energy, potential energy, power and use the concept of ... – PowerPoint PPT presentation

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Title: How is Work and Power Related? Chapter 5 Work and Power


1
How is Work and Power Related? Chapter 5 Work and
Power
  • Goals define and calculate work, energy, kinetic
    energy, potential energy, power and use the
    concept of conservation of energy

2
What is Work? Section 5.1
  • Work is a transfer or conversion of energy
  • transfer occurs when a force is applied in the
    direction of the force force
    mass x acceleration (g)
  • conversion occurs from one form of energy to
    another
  • mechanical, thermal, electrical, radiant,
    nuclear and chemical
  • W F x d W F x d cos ?

3
Simple Machines demonstrate the concept and
calculations of Work
  • Simple Machine- device that makes work easier
  • multiply force OR distance
  • Increasing force or distance are at the expense
    of the other variable
  • Energy is conserved in an ideal situation
    no friction
  • Work in would equal Work out in another words F
    x d (in) F x d (out)
  • Work in is done on the machine and Work out is
    done by the machine

4
  • R ---2m-----f--------4m------- E
  • MA 2
  • R 40N---------f------------------- E 20N
  • MA 2
  • MA Fr / Fe or
  • MA Xe / Xr
  • Levers include 1st, 2nd, 3rd, classes, wheels and
    axels and pulleys
  • Pulley- grooved wheel and a rope MA the number
    of strands supporting resistance

5
  • Inclined Planes include ramps, wedges and screws
  • Gears- toothed wheels MA ratio of teeth of each
    gear increase force or speed of rotation
  • Efficiency- ratio of work out to work in
  • eff W out / W in

6
What is Energy? 5.2
  • Energy ability to cause a change
  • to do work work transfer of energy
  • 6 forms of energy and two states of energy
  • Kinetic motion
  • W F x d
  • m x a x ?X a ?X vf² - vi² / 2
  • m x vf² - vi² / 2
  • ½ m v²
  • increase mass vs increase velocity v²

7
  • Work Energy Theorem
  • transfer of energy by a force through a distance
  • transfers Kinetic Energy
  • Work ?KE
  • KE f KE i
  • Units KE ½ mv²
  • kg m²/s²
  • N m
  • J

8
What is Potential Energy?
  • Potential Energy state of energy where a change
    is stored
  • position relative to a measured height
  • gravitational potential energy
  • PE m g h weight m g
  • kg m/s² m N
  • N m
  • J

9
  • Elastic potential energy energy stored in an
    object stretched or compressed
  • Spring ex. spring scale
  • PE elastic ½ k x²
  • k spring constant
  • x distance stretched

10
How is Energy Conserved ?
  • Conserved energy is not gained or lost within a
    system
  • only converted or transferred
  • Mechanical Energy is the sum of the KE and the PE
    in a system
  • the exception is friction that converts some ME
    into heat that is nonmechanical
  • ME i ME f KE PE KEtotal
  • ½ mv² mgh ½ mv² mgh
  • ex. Falling rock PE to PEKE to KE

11
What is the Rate at which work is done?
  • Power the rate at which work is done or energy
    converted or transferred
  • P ?W / t
  • F x d / t
  • F x v
  • mgh / t or ½ mv² / t
  • units P W / t
  • J / s
  • watts 1000 w
    kw
  • 1 hp 746 w

12
  • YOU have the POWER
  • To get the WORK done
  • And
  • Accelerate on this next Exam
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